Reflector antenna inflatable with foamed plastic



June 3, 1969 J. H. PESSIN 3,448,456

REFLECTOR ANTENNA INFLATABLE WITH FOAMED PLASTIC Filed Sept. 12, 1966INVENTOR JACQUES H. PESSl/V AGED/VT ATTORNEY United States Patent3,448,456 REFLECTOR ANTENNA INFLATABLE WITH FOAMED PLASTIC Jacques H.Pessin, Ellicott City, Md., assignor, by mesne assignments, to theUnited States of America as represented by the Secretary of the NavyFiled Sept. 12, 1966, Ser. No. 578,893

Int. Cl. H011; 1/40 U.S. Cl. 343-873 8 Claims The invention relates toan improved antenna system and method, and more particularly to animproved antenna system and method that employs supporting plastic foam.

Inflatable or collapsible antennas have seen considerable use in radarand other electrical magnetic radiation applications, especially wherethe installation is temporary and must be reinstalled at eitherlocations at frequent intervals. The inflatable types have seenespecially wide use because they are light in weight, easily portableand easily installed and reinstalled and so have seen considerable usein highly mobile field radar installations. Inflatable antennas however,must be continuously pressurized during operation from a source of gas,such as, air from a blower to replace the gas lost by leakage. The airsource must be controlled in order that the antenna be supported by aconstant pressure, to avoid variations in the shape of the antenna whichwould change its radi-a tion pattern. Additionally inflatable antennashave structural deficiencies inherent in any gaseous inflated shapewhich allow the antenna to flex and change shape under the influence ofwind or ice loading. This change in shape effects a change in radiationpattern of the antenna and thereby reduces the accuracy of the entiresystem.

The improved antenna system of the invention eliminates theaforementioned problems associated with gaseous inflated antennas whileretaining their light weight and portability attributes. The inventionprovides an antenna system comprising of an outer balloon element and aninner filler element. The outer balloon element is of similarconstruction to that commonly found in inflatable antennas and hassimilar reflective characteristics. The outer balloon element of theinvention however, is adapted for use with the unique inflating methodof the invention. The invention employs a plastic foam inflation thatmakes the antenna self supporting, rigid, and not dependent oncontinuous air supply.

It is therefore an object of the instant invention to provide animproved light weight and portable antenna system.

It is another object of the invention to provide an improved lightweight and portable antenna system that does not require a continuousair supply for inflation.

It is a further object of the invention to provide an improved antennasystem that employs a plastic foam for support.

It is still another object of the invention to provide an improvedantenna system that employs a plastic foam for support that may bediscarded when the antenna is moved.

It is a still further object of the invention to provide an improvedprocess for erecting antenna systems that employs a foaming processwithin an antenna balloon.

It is an additional object of the invention to provide an antenna systemof light weight construction that employs plastic foam that incorporatesair filled voids within the foamed plastic.

These and other objects and many of the attendant advantages of theinvention will be more readily understood by reference to the followingdetailed description of one specific embodiment thereof when consideredin connection with the accompanying drawing, wherein:

FIG. 1 is a perspective view of the antenna system of the invention;

FIG. 2 is a cross sectional view taken along line 22 of FIG. 1 andshowing one alternative embodiment of the interior construction of theantenna supporting foam;

FIG. 3 is an additional cross sectional view also taken along sectionline 2-2 of FIG. 1 and showing a second alternative embodiment of theinterior construction of the antenna supporting foam;

FIG. 4 is a cross sectional view taken along line 44 of FIG. 2, andshowing construction of the outer envelope of the antenna system of theinvention.

Referring now to the drawing there is shown in FIG. 1 the antenna system10, mounted on a suitable support 12 having a horn 14 and secondaryreflector 16 mounted thereon. At one end of the antenna envelope orballoon 18 there is shown, indicated generally by numeral 20, an endseam. The seam in the instant embodiment is shown to comprise anoverlapping continuous sealing strip 22, such as a Velcro strip, and aplurality of buckles 24. The strip provides a sealing function whereasthe buckles are designed to give strength to the seam and will bedescribed more fully hereinafter.

Referring now to FIGS. 2 and 3, there are shown two alternativeembodiments for the interior of the antenna system 10. In cross sectionthe antenna system 10 is shown to contain a filler material 26. In thepreferred embodiment this filler material is comprised of light weightfoamed plastic. The particular foam employed would be chosen for itslight weight characteristics and ease of foaming in situs and could be,for example, polyurethane. The foam is contained within a thin plasticinner balloon 28 such as Pliofilm. This balloon is employed to make thefoamed filler an independent package which may be removed upon antennadismantling and its use will be described more fully hereinafter. FIG. 2shows one embodiment of a method to reduce the over all weight of theantenna supporting foam filler. This embodiment employs an elongatedvoid creating balloon 30, which is inflated within the outer bag 28prior to foaming and thereby creates a void within the foam material andallows a considerable reduction in weight. The modification of FIG. 3differs from that shown in FIG. 2 only in the number of void creatingballoons employed in the weight reduction process. Balloons 32, 34 and36 are shown to be of varying size to substantially conform to theover-all shape of the inflated antenna. By the use of a plurality ofthese void creating balloons in this fashion the overall weight of theantenna system may be reduced still further while retaining adequatefoam to support the antenna system. Both FIGS. 2 and 3 also show inletnozzle 38 and pressure release valve 40 and shaping rods 42 and 44 to bedescribed hereinafter. Indicated diagrammatically in FIGS. 2 and 3 isthe main reflector element 46 which directs the transmitted and receivedenergy to and from the secondary reflector element 16. One suitableconfiguration for this reflector element is shown in FIG. 4. The outeror protective material 48 is bonded to a first aluminum foil reflectivelayer 50 which is in turn bonded to a second protective or strengthlayer 52. This second layer is bonded to a final aluminum foilreflective layer 54. In the assembled condition these four bonded layersare in intimate contact with the Pliofilm bag 28 that contains the foamfiller material.

The antenna system is readied for operation by erecting the mast 12 andaffixing thereto by suitable means, not shown, the outer balloon 18which contains inner balloon 28. If void creating balloons are to beemployed, they are inflated with for example, air and inserted withinthe inner balloon through the opening 20 and a similar opening withinthe inner balloon. The openings are then secured which in the case ofthe outer balloon may be accomplished by the strip 22 and attachingclamps 24. Foam generating apparatus is then connected to nozzle 38 andthe plastic foam components are mixed and forced into the antennasystems interior. The nozzle passes from the exterior of theantennathroug'h, the outer balloon and inner balloon but is afiixed tothe outer bag only to provide for the later removal of the inner balloonand its contents. If the foam to be employed is polyurethane, forexample, the foam generating apparatus could comprise tanks forisocyanate and polyol, means to force the iso cyanate and polyol to amixing head and means to deliver the reacting isocyanate and polyolsubsequent to mixing, to the nozzle 38. As the plastic foam componentspass through the nozzle and enter the balloons they expand and surroundthe void creating balloons. As filling continues, the antenna is formedinto its designed shape. Pressure relief valve 40 allows the escape ofentrapped air as it becomes pressurized by the expanding foam butretains adequate pressure to force complete expansion of the balloonthereby insuring accurate shaping. Shaping rods 42 and 44 are providedto insure accurate shaping of the bottom portion of the antenna systemand may be affixed to the outer balloon for retention therewith. Whenfoaming is complete the connection to nozzle 38 may be removed and thefoam allowed to harden, Upon hardening the antenna system becomes selfsupporting and not dependent on the seal at opening or the integrity ofthe outer balloon elsewhere. At this stage the system is ready foroperation and needs no further attention until disassembly becomesnecessary. The foamed material has substantially no effect on thetransmission or reflection of radio waves from the primary reflector 46and the secondary reflector 16. In other words the foamed material issubstantially transparent to radio waves and very little absorptiontakes place by transmission through this medium.

When it becomes necessary to disassemble the antenna system it is merelynecessary to unlatch clamps 24 and zip open the strip 22 to expose thefoamed material contained within the inner bag 28. The opening 20 islarge enough to allow the inner bag with its rigid foam contents to beslid from the outer bag 18. The foamed material can be disposed of atthe site and it is not necessary to transport it with the remainder ofthe antenna system since it is inexpensive and a new foamed interior canreadily be generated at the next site of operation. Thus the weight andvolume of material necessary to be transported in support of the antennasystem is kept to a minimum. Only the expensive and difiicult to replaceouter antenna balloon 18 need by retained and that may be collapsed to asmall volume for shipping.

As will be clear from the foregoing description the outer balloon 18 isa critical portion of the entire antenna system. The outer covering mustbe of sufficient strength to retain its shape and resist abrasion andgeneral deterioration due to the exposure of the elements. Fiberglascloth has adequate strength and weathering characteristics and isgenerally suitable to the purposes of the invention. Additionally it iswithin the concept of the invention to employ a Mylar material with aDacron scrim, the Mylar being employed for its water and gas imperviousnature and the Dacron scrim for strength. This combination is lighterthan the Fiberglas combination and may be preferable where weight is anoverriding consideration. The material may be pleated as shown in FIG. 1to achieve the proper shape.

The construction of a preferred embodiment of the outer balloon in thesection having the primary reflector is shown in section in FIG. 4. Ascan be seen from this figure there are two layers of strength material48 and 52 which may be either of the Fiberglas or Mylar- Dacronmaterial. Two layers are employed in this region in order to separatetwo layers of reflective material. This reflective material in theinstant embodiment is of the nature of aluminum foil, that is, very thinaluminum sheets sandwiched in the case of sheet 50 between layers 48 and52 and in the case of sheet 54 being bonded to layer 52 and protected onits other side by the inner balloon element 28. The purpose of employingtwo reflective layers is to avoid any change in the reflectivecharactistics of the antenna when small surface discontinuities orcracks occur in the reflective material. It should be noted that theparticular configuration of the reflector portion of the antenna systemhas been described not by way of limitation but only as a preferredexample due to its superior wearing characteristics. Other multilayerand single layer reflectors could be employed with the antenna system ofthe invention for example, a single sheet of aluminum could be aflixedto a single layer outer covering of Fiberglas or Mylar-Dacron.Additionally it should be noted that the rods 42 and 44 are notessential to the invention, although their use is preferred tostrengthen the expanded structure and to stabilize the form to preventchanges in contour at the point of attachment. Further it is obviousthat many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed is:

1. A light weight portable antenna system comprisan outer balloon membercontaining a light weight plastic foam; said outer balloon member beingflexible and incorporating over a portion of said outer balloon membermeans for reflecting radio frequency energy;

said outer balloon member including a resealable seam,

whereby said plastic foam may be removed from said outer balloon member.

2. The light weight portable antenna system of claim 1 wherein:

said light weight plastic foam contains at least one void whereby theweight of said antenna system is reduced.

3. The light weight portable antenna system of claim 2 further includingan inner balloon member surrounding said light weight plastic foam andremovable therewith.

4. The antenna system of claim 1 wherein:

the outer balloon material is comprised of glass fiber cloth.

5. The antenna system of claim 1 wherein the outer balloon material iscomprised of a water and gas impermeable material with a strengtheningscrim.

6. The antenna system of claim 3 further including a filling nozzle anda pressure relief valve attached through said outer and inner balloonswhereby said light weight plastic foam may be forced-into said balloon7. The antenna system of claim 1 wherein said means for reflecting radiofrequency energy at least one layer of aluminum bonded to said outerballoon member.

8. The antenna system of claim 1 wherein said means for reflecting radiofrequency comprises a plurality of aluminum layers separated by flexiblematerial;

whereby the reflective properties of said means for reflecting radiofrequency energy are not effected by discontinuities in a single one ofsaid aluminum layers.

References Cited UNITED STATES PATENTS 2,731,055 1/1956 Smith 343-872ELI LIEBERMAN, Primary Examiner.

U.S. Cl. X.R. 343--781, 915

1. A LIGHT WEIGHT PORTABLE ANTENNA SYSTEM COMPRISING: AN OUTER BALLONMEMBER CONTAINING A LIGHT WEIGHT PLASTIC FOAM; SAID OUTER BALLOON MEMBERBEING FLEXIBLE AND INCOR PORATING OVER A PORTION OF SAID OUTER BALLOONMEMBER MEANS FOR REFLECTING RADIO FREQUENCY ENERGY; SAID OUTER BALLOONMEMBER INCLUDING A RESEABLABLE SEAM, WHEREBY SAID PLASTIC FOAM MAY BEREMOVED FROM SAID OUTER BALLOON MEMBER.